This invention relates to an adaptive phase and amplitude distributor which is based on circular W/G polarizers and rotating joints interconnected according to a joint-polarizer-joint-polarizer etc. configuration and on an orthomode.TM. transducer placed at the output to separate the orthogonal components of the electromagnetic field.
The invention belongs to the microwave field. It finds a most advantageous application within an antenna system, preferably satellite borne, where the transmitter power needs to be distributed over many elementary radiators having pre-determined amplitude and phase to acheive desired radiation patterns.
This distributor derives from an existing system, simplified and adapted, originally conceived for different purposes, known as "soft fail" and used successfully for quite some time by the owner of the Italian patent No. 1 149 024.
The existing soft fail solution, from which the distributor here presented derives, combined the power of two transmitters (350 W nom each at 18 GHz) adaptively to deliver it to an antenna without losses. If the power and phase ratio of the two transmitters vary, the soft fail device would adapt to the situation arising so that the sum of the two transmitters power would continue to feed the antenna and not the "dummy load", as would have happened by adopting a non adaptive combiner (FIG. 4).
The device which is presented hereby, and which we shall refer to as APAD (Adaptive Phase and Amplitude Distributor) works, in principle, in an opposite manner; it takes the power from one single source and it distributes it with presettable amplitude and phase to two loads, such as two foods.
If the soft fail works, according to the reciprocity principle, it must also operate as a combiner; moreover the circuit may be simplified because one of the two OMTs may be eliminated (FIG. 1). Losses, which were already low in the soft fail, are here almost halved.
In general, when the radiation pattern of satellite borne antennae needs to be reconfigured, an array of small feeds is placed on the local plane of a reflector antenna. By exciting such feeds in phase and amplitude, different radiation patterns of the antenna can be obtained.
The APAD is a device based on two rotating joints and polarizers, which distributes the power produced by a microwave source between two separate loads with any phase and amplitude relationship and low losses.
The distribution ratio is a function of the rotating angle of the polarizers, which are therefore the controlling variables.
By utilizing more than one identical independently controlled device, a transmitter power distribution network for a feed array can be obtained with any variable amplitude and phase pattern.
Until now similar but bulkier devices were available. The prior devices, affected by greater losses, were based upon a double rotating joint which could phaseshift the signal of one path against the other by 180.degree. and were further based on an additional phase shifter having a different structure. The greater losses were due to the phase shifter.
As we have said, the APAD may be compared to the previous soft fail 180.degree. polarizer, but cut into half lengthwise and modified to become two 90.degree. polarizers.
In this manner the two sections of the 180.degree. polarizer once made independent, perform the same function as the non-sectioned polarizer joined to the phase shifter.
Furthermore, this device suffers lower losses by virtue of the fact that it makes use of one single OMT (Orthomode.TM. Transducer) in its original configuration.
The elimination of the phase shifter also results in a weight reduction.